Gas springs are used in a variety of applications to selectively position a movable member with respect to a static member. The gas spring is formed from a hollow cylinder having an open end and a closed end. The closed end is typically attached to the static member, such as through a pivotable mounting arrangement, so as to provide a stable base for the gas spring. The open end of the cylinder defines a circular opening that is adapted to receive an elongated rod, which includes an outer end adapted for connection to the movable member. The rod extends through the opening into the cylinder, and includes an inner end which is mounted to a piston located within a piston cavity defined by the hollow cylinder. The piston is movable within the piston cavity in response to extension and retraction of the rod caused by movement of the movable member relative to the stationary member. In this manner, the operative length of the gas spring is controlled by the length of the piston cavity, which entails the majority of the length of the cylinder.
The rod extends into the interior of the cylinder through a sealing arrangement that serves to retain a volume of pressurized gas, such as nitrogen, and lubricating fluid within the cylinder. The pressurized gas acts on the piston to control the movement of the rod with respect to the cylinder and to selectively maintain the rod in position relative to the cylinder. The sealing arrangement is positioned adjacent the open end of the cylinder. In a prior art construction, the sealing arrangement includes a rod guide, a washer, a first fluid seal and a second fluid seal.
In the prior art construction the rod guide is positioned immediately against the open end of the cylinder and defines a central opening through which the rod extends. The rod guide is formed of a generally rigid material that serves to retain the rod in proper axial alignment with respect to the open end of the cylinder such that the rod may slide freely through the open end.
Opposite the open end, a metal washer is positioned against the rod guide. The metal washer is formed of a rigid metal such as low carbon steel in a process separate from the formation of the remainder of the sealing arrangement. To retain the metal washer in position within the sealing arrangement, after its manufacture the washer is treated with a zinc phosphate coating which allows a subsequent adhesive coating applied between the sealing arrangement components and the metal washer to adhere the washer to the components of the sealing arrangement. The washer provides stiffness and support to the sealing arrangement and maintains the axial and radial position of the sealing arrangement when used in a dynamic gas spring application. Furthermore, because the washer is made of a rigid metal, the washer is less permeable to nitrogen gas than the rest of the sealing arrangement and acts as a barrier between the nitrogen gas inside the cylinder and the exterior of the cylinder.
The first fluid seal is positioned against the metal washer opposite the rod guide. The first seal includes a central opening aligned with the opening in the rod guide and sealingly engages the interior surface of the cylinder about its circumference. The first seal also sealingly engages the rod as the rod extends through the central opening to prevent a lubricant, that coats the exterior of the rod, and the pressurized gas from escaping from the cylinder.
The second fluid seal abuts the first fluid seal opposite the washer. The second seal defines a lubricating fluid reservoir having a central bore aligned with the opening in the first seal through which the rod extends. The reservoir is closed opposite the bore by the first seal and is filled with the lubricant that coats the exterior surface of the rod. This construction allows the rod to slide freely through the opening in the first seal, the bore in the second seal and the opening in the rod guide. The second seal also sealingly engages the rod and the interior surface of the cylinder to maintain the pressurized gas within the piston cavity.
The sealing arrangement is retained in position against the open end of the cylinder by a crimp in the cylinder body that abuts the second seal adjacent the bore. The crimp extends inwardly a sufficient distance to prevent the sealing arrangement from sliding along the interior surface of the cylinder away from the open end.
To develop a washer supported elastomeric seal, a zinc phosphate coating is initially applied to the metal washer. The elastomeric seal is then molded over the washer in a controlled environment and the bonding is achieved during the curing process of the elastomer. To assemble the sealing arrangement in a gas spring, the components, such as rod guide, first seal, and second seal, are positioned against each other in a desired configuration to form a specific sealing arrangement. The sealing arrangement may then be positioned as a whole within a particular gas spring assembly.
While providing a reliable sealing arrangement for the gas spring, this prior art sealing arrangement has certain drawbacks. First, the multitude of parts comprising the sealing arrangement requires a slow and complex process in order to properly assemble the sealing arrangement. Second, bonding of the metal washer to the first seal involves a meticulous process in order to achieve a bond strength that is adequate to meet the functional requirements of the sealing arrangement. This process greatly increases the cost of production of the sealing arrangement and slows the overall production of the sealing arrangements. Finally, the structure of the prior art sealing arrangement may allow a certain amount of the pressurized gas held within the cylinder to permeate through the sealing arrangement and escape from the cylinder, which adversely effects the ability of the gas spring to function in the desired manner.
Therefore, it is desirable to develop a seal assembly for use in a gas spring that does not require the expensive and complex process of bonding elastomeric parts to metal parts within the assembly. The seal assembly should contain a minimum of individual parts overall, which should be able to be produced in a fast and efficient manner. Further the seal assembly should be formed in such a manner as to greatly reduce the permeability of the pressurized gas through the seal assembly to extend the useful life of a gas spring in which the seal assembly is utilized.